1. Field of Invention
Embodiments of the invention generally relate to spectroscopy. More specifically, at least one embodiment relates to a hand-held IR spectrometer.
2. Discussion of Related Art
Many bench-top instruments exist that would find a much wider application if they could be reduced to a hand-held tool. The hand-held barcode scanner represents one hand-held tool that has been developed from a bench-top instrument. The barcode scanner was a large instrument used at grocery checkout stands when it was first developed. Subsequently, however, the barcode scanner has become a hand-held tool used for reading barcodes wherever they occur, for example, reading barcodes for the purpose of inventory tracking. The development of a hand-held instrument from a bench-top instrument generally requires a substantial reduction in the size and weight of the instrument. Because portable hand-held tools generally rely on battery power sources, efficient power consumption is also important to reducing weight by reducing the amount of power required for extended operation. That is, given the generally heavy weight of battery power sources, efficient power consumption reduces the amount of battery power required for extended operation and consequently may result in a substantial reduction in the weight of the hand-held instrument. In addition, to be useful, the hand-held instrument should maintain a degree of performance similar to that of the bench-top instrument.
As used herein the term “hand-held” when used to describe an instrument or tool means a device that can be comfortably held by a user with one or two hands, for example, while operating the device. A barcode scanning wand provides one example of a commonly used hand-held device. A hand-held tool may include any of a power cord, a cord that tethers the hand-held device to a main device, and/or a battery pack or other portable power source that provides power for the tool's operation.
Spectroscopy is the study of the spectral characteristics of matter, and the use of such spectral characteristics to obtain qualitative and/or quantitative information about samples of matter (also referred to herein simply as samples). Conventional spectroscopic techniques may utilize absorption spectra of matter or reflectance spectra of matter, as determined by the energy level structures of constituent atoms and molecules, to determine to the presence and/or quantity of such atoms and molecules in the matter.
Instruments used to measure reflectance spectra may be referred to as reflectance spectrometers. In reflectance spectrometers, information concerning the composition of a sample is obtained by projecting light onto a surface of the sample and measuring the amount of the light that is reflected by the sample as a function of wavelength. Because atoms and molecules have unique reflectance spectra (sometimes referred to as spectral signatures), it is possible to determine the presence and/or quantity of constituents of the sample of matter, for example, by determining reflectivity as a function of wavelength. As one of ordinary skill in the art would understand, use of the term “wavelength” herein, such as when referring to a wavelength of light that is detected or a wavelength of light from a source, refers to light of the indicated wavelength and light from a finite band of wavelengths around said wavelengths, as may be determined by the laws of physics and/or conventional design practices.
There exist numerous types of conventional reflectance spectrometers. Conventional reflectance spectrometers typically have the following features in common: a light source that covers a desired band of wavelengths from which spectral signatures are to be determined; a detector (or detector array) that is sensitive to light in the desired wavelength range; and optical componentry (e.g., a focusing element) that collects the light after it interacts with the sample of matter and directs the collected light onto the detector. Additionally, because information is present in the reflected light as a function of incident wavelength, an apparatus providing wavelength selection is typically included.
Conventional reflectance spectrometers may employ any of several different wavelength selection and detection techniques, for example: a monochromator-type spectrometer projects wavelengths of light sequentially onto a sample; an optical multichannel analyzer projects multiple wavelengths of light from a broadband light source onto a sample simultaneously, and then projects the reflected light onto a detector array; and, a filter wheel spectrometer projects light from a broadband source though each of a series of fixed optical filters in a sequential manner (e.g., by locating the filters on a motor-driven chopper wheel), to illuminate a sample with a sequence of different wavelengths of light.
An instrument that currently has a wide range of uses as a bench-top instrument is the IR spectrometer. The IR spectrometer is employed as an analytical instrument in the to food, pharmaceutical, petroleum, and agriculture industries for identification and quantification of chemical compounds. The IR spectrometer can also be employed in many other applications. Although many of the applications for the IR spectrometer would benefit from the availability of a hand-held IR spectrometer, none exist at present. Further, there have been few attempts to produce a hand-held IR spectrometer because of the size and power requirements of components employed in conventional IR spectrometers. One example of a “portable” IR spectrometer is the Luminar 5030 by Brimrose [www.Brimrose.com]; however, this device still requires 90 watts of power and is not hand held because it weighs tens of pounds.
The optical requirements and/or the cooling systems of current IR spectrometer designs are generally incompatible with a lightweight, portable instrument. For example, a conventional monochromator IR spectrometer includes a grating, a heavy rigid structure to maintain accuracy while the grating is being rotated, and a drive motor to rotate the grating. The size, weight and power consumption that results from these components reduces the likelihood that they can be included in a hand-held instrument. Similarly, conventional Fourier transform IR spectrometers also include moving parts and require heavy, rigid structures and a drive motor to operate accurately. The optical multi-channel analyzer or diode array spectrometer has no moving parts; however, in the IR part of the spectrum, the analyzer requires that the detector be cooled to meet minimum performance standards. The required cooling system includes a heat sink and thermoelectric cooler that consume a relatively large amount of power. Thus, the power consumption of a multi-channel IR analyzer is too great for it to be employed as a hand-held instrument because a large power source would be required for its operation.